1. Field of the Invention
The invention relates to a display control system and, more particularly, to a display apparatus having a display device which uses, for example, a ferroelectric liquid crystal as an operation medium for display updating and which can hold the updated display state by applying an electric field or the like. The invention also relates to a display control system comprising a display control apparatus.
2. Related Background Art
Generally, a display apparatus as information display means for performing a visual expressing function of information is used in an information processing system or the like. A CRT display apparatus is well known as such a display apparatus. Since the CRT needs, particularly, a certain extent of length in the thickness direction of a display screen, however, its volume is large and it is difficult to miniaturize the whole display apparatus. A degree of freedom when using the information processing system using such a CRT as a display, namely, a degree of freedom of the installing location, portability, or the like is lost.
A liquid crystal display (hereinafter, simply referred to as an LCD) can be used as a device for compensating such a drawback. Namely, according to the LCD, the whole display apparatus can be miniaturized (particularly, it can be made thin). Among such LCDs, there is a display using liquid crystal cells of the ferroelectric liquid crystal (hereinafter, abbreviated to an FLC) mentioned above (such a display is hereinbelow referred to as an FLCD, namely, FLC display). One of the features of the FLCD is that the liquid crystal cell has a preservation performance of the display state for application of an electric field. Namely, in an FLCD, the liquid crystal cell is thin enough and a molecule of the elongated FLC in the liquid crystal cell is oriented to the first or second stable state in accordance with the applying direction of the electric field and maintains each orientation state even when the electric field is eliminated. The FLCD has a memory performance owing to the bistability of such an FLC molecule. Such FLC and FLCD have been described in detail in, for example, Japanese Laid-open Patent Application No. 63-243922, corresponding to Japanese Patent Application No. 62-76357.
Since the FLCD has the memory performance, in case of driving the FLCD, unlike the CRT or other liquid crystal displays, a surplus time is produced in a period of time for a continuous refresh driving of the display image frame. Separately from such a continuous refresh driving, a partial rewrite driving to update the display state of only the portion corresponding to a change on the display image frame can be performed.
In the FLCD, in accordance with a display information output request signal that is outputted from the display apparatus, by outputting a line address corresponding to the number of lines in the vertical direction of the display image frame and pixel information of the lines, the partial rewrite driving is executed, thereby improving an apparent display speed.
However, in the conventional FLCD control system, since the display apparatus side requires the output of the display information at a certain predetermined period, the following problems occur. For example, in the case where a resolution of an effective display region which is used for display on the image frame of the FLCD has a plurality of display formats such as [1024 pixels (lateral direction).times.768 lines (vertical direction)], [800 pixels (lateral direction).times.600 lines (vertical direction)], and the like, when the display format is switched during the display operation, the image in the way of the updating operation is displayed until the contents in a video RAM (hereinafter, simply referred to as a VRAM) in which the information to be displayed has been stored are updated to the contents in the display mode after completion of the change. Consequently, a disturbance of the image instantaneously occurs.
As means of solving the problems as mentioned above, there is easily considered means such that until the contents in the VRAM are updated to the contents of the changed display format, the display information is not transmitted on the FLCD interface side even if a transmission request of the information to be displayed by the FLCD arrives.
In case of using such means, however, in spite of the fact that the FLCD side has requested the transmission of the information to be displayed, since no display information is transmitted from the FLCD interface side, the FLCD side is held in the standby state. There occur various troubles such that other processes cannot be executed in the FLCD, the FLCD is not recovered in the standby state in the worst case, and the like.